Such a phase comparator is known from DE 40 25 307 A1. In principle, the distance in time is measured between two equal-phase points of the signals being compared. The phase difference of the passage through zero is determined from the thus assumed analog signals. The slopes are the reference points when digital signals are being compared. If rising zero passages or slopes of one signal are compared with falling zero passages or slopes of the other signal, 180 degrees must be added to the obtained phase difference, which may be desirable for many applications. With the known comparator, a gate is opened by a signal whose reference phase occurs first; the other signal closes the gate. A counter counts the intermediate pulses of a timer. In the known example, the time pulse is coupled to one of the two signals that acts as reference signal in such a way, that its frequency is an integral multiple of the reference signal's frequency. For example, when the frequency of the timer is 360 times that of the reference signal frequency, the counted pulses directly provide the phase difference in degrees.
With the known comparator, the smallest measurable phase difference is one degree. A finer resolution can only be achieved by increasing the pulse frequency of the time pulse. However, it has relatively narrow limits. Furthermore, with the known comparator there is the problem of coincidence suppression of small phase differences, which also prevents measuring the smallest differences.